The present invention relates to an image forming apparatus that makes a cleaning toner image to be born on the surface of an image bearing element and a transfer element, after which the surfaces of the image bearing element and the transfer element are cleaned by a cleaning element.
Some electrophotographic image forming apparatuses are configured to transfer a toner image that is born on an image bearing element, such as a photoreceptor drum and an intermediate transfer element, onto a sheet in a transfer position between the image bearing element and the transfer element. Residual toner that remains on the surfaces of the image bearing element and the transfer element after the toner image is transferred to the sheet is removed by the cleaning element by the next image forming process.
For example, when the image bearing element is being cleaned and the residual toner is low, if the surface of the image bearing element contacts the cleaning element to be cleaned, friction will increase between the surface of the image bearing element and the cleaning element and will damage the surface of the image bearing element.
In an attempt to overcome such problems, some conventional image forming apparatuses, as disclosed in Japanese Patent Laid-Open Publication No. 2006-251138 for example, supply cleaning toner in an amount corresponding to the density of an image formed in the latest image forming process to the surface of the image bearing element before making the cleaning element contact the surface of the image bearing element.
However, at the time when the image bearing element and the transfer element are cleaned, damage can also be inflicted to the surfaces of the image bearing element and the transfer element due to paper powder that exists between the cleaning element and the surfaces of the image bearing element and the transfer element; and the damage to the surfaces of the image bearing element and the transfer element is greater as the amount of paper powder that adheres to the surfaces of the image bearing element and the transfer element is larger. Therefore, according to the amount of paper powder that adheres to the surfaces of the image bearing element and the transfer element, it is necessary to adjust the amount of cleaning toner.
The paper powder is generated by contacting a sheet with feed elements, such as a pick-up roller, a feed roller and a feed guide, while a sheet is fed from the sheet feed cassette to a transfer position through a feed path. More particularly, since the pick-up roller contacts the surface of a stationary sheet, the paper powder is generated mainly from the pick-up side of the sheet that the pick-up roller contacts while, in the transfer position, the paper powder easily adheres to either one of the image bearing element or the transfer element to which the pick-up side of the sheet is opposed.
Some image forming apparatuses are equipped with a plurality of feed paths including: a first feed path in which the sheet is fed so that the pick-up side is opposed to the image bearing element in the transfer position; and a second feed path in which the sheet is fed so that the pick-up side is opposed to the transfer element. In such image forming apparatuses, the amount of paper powder that adheres to each of the image bearing element and the transfer element varies according to through which the feed path the sheet is fed. If the amount of toner for the cleaning toner images that are supplied to each of the surfaces of the image bearing element and the transfer element is fixed, damage to the surfaces of both the image bearing element and the transfer element cannot be reliably prevented.
In view of the foregoing, an object of the present invention is to provide an image forming apparatus that can ensure that damage is prevented to the surfaces of both an image bearing element and a transfer element, by adjusting the amount of cleaning toner that is supplied to each of the image bearing element and to the transfer element based on the number of sheets that are fed into each of a plurality of feed paths.